1. Field of the Invention
The invention pertains to a large mobile crane with an undercarriage, a drive unit, a superstructure, one or more control stations, at least two main booms, at least one derrick boom, at least two lifting devices and counterweights, either separate or mounted on the basic machine.
2. Description of the Related Art
Various solutions are known for lifting extremely heavy loads exceeding the capacity of the various current mobile crane designs, large numbers of which are on the market.
It is possible, for example, with the use of the reliable mechanical elements and materials already available for constructing cranes, to build a very large lattice-boom crawler crane whenever desired. As a result of the necessary size of the individual components, however, considerable problems are encountered in the production of the castings in particular, such as the base plates and cable drums as well as the hydraulic components. Although technological limits are reached in some cases, economic limits are reached in all cases, and all of the large cranes thus obtained would include individual pieces difficult to move from one work location to another. The large components present significant problems with respect to transport and handling such as the ability to be driven along ordinary roads and to pass under bridges. An alternative solution, namely, dividing the individual basic components into smaller components, would lead to additional, relatively high costs. Overall, a large machine of this type would be extremely expensive and, as experience has shown, would represent a commercial prototype.
Ring-lift cranes represent a different approach to the lifting of heavy loads. These usually have a large boom or a double-boom system (arranged in parallel or in the shape of an “A”), which are supported on the ground by way of a circular track. In the meantime, several patents have been granted for cranes of this type such as U.S. Pat. No. 4,103,783 and U.S. Pat. No. 4,196,816. The advantage of the ring-lift crane is that much higher load moments can be reached than is possible with crawler cranes. The disadvantage is that ring-lift cranes cannot be moved with a suspended load, and even without a load they can be moved only with considerable effort. In addition, they can make use of only a few components of standard production cranes. They must therefore usually be assembled on site and thus block the progress of the construction work during the tedious assembly and disassembly phases.
So-called derrick cranes are also known. Here a main boom is paired with a derrick boom, the two booms being mounted on the superstructure of a mobile undercarriage or on a stationary foundation.
The extremely large dimensions of all these machines, as previously mentioned, is disadvantageous, because they cause problems during transport and assembly/disassembly. They also suffer from poor lateral stability (especially serious in the case of loads with large surface areas exposed to the wind) because of the unfavorable relationship between the large size of the machine and the short distance between the tracks of the crawler-type carriage